Submission #1251467

#	Time	Username	Problem	Language	Result	Execution time	Memory
1251467		InternetPerson10	Triple Peaks (IOI25_triples)	C++20	75.29 / 100	1481 ms	95300 KiB

triples

#include "triples.h"
#include <bits/stdc++.h>

using namespace std;
typedef long long ll;

unordered_set<int> sum_ct[400001];
unordered_set<int> dif_ct[400001];

long long count_triples(vector<int> v) {
    int n = v.size();
    auto is_in_range = [&](int x) {
        return (0 <= x && x < n);
    };
    auto try_bound = [&](int l, int r) {
        int x = min(v[l], v[r]);
        assert(x < r-l);
        int g = max(v[l], v[r]) - min(v[l], v[r]);
        int ans = 0;
        if(v[l+x] == g) ans++;
        if(v[r-x] == g) ans++;
        if(l+x == r-x && ans == 2) ans--;
        return ans;
    };
    ll tot = 0;
    // peak on the left or right
    for(int i = 0; i < n; i++) {
        if(is_in_range(i + v[i]) && v[i+v[i]] < v[i]) {
            tot += try_bound(i, i+v[i]);
        }
        if(is_in_range(i - v[i]) && v[i-v[i]] < v[i]) {
            tot += try_bound(i-v[i], i);
        }
    }
    // peak on the middle, 2-5--3
    for(int i = 0; i < n; i++) {
        if(is_in_range(i + v[i]) && is_in_range(i + v[i + v[i]])) {
            // probably remove overcounts
            if(v[i] + v[i + v[i + v[i]]] == v[i + v[i]] && v[i] != v[i + v[i + v[i]]]) tot++;
        }
    }
    // cout << "So far tot is " << tot << endl;
    // peak on the middle, 3-5--2
    for(int i = 0; i < 2 * n; i++) {
        sum_ct[i].clear();
        dif_ct[i].clear();
    }
    for(int i = 0; i < n; i++) {
        sum_ct[i + v[i]].insert(v[i]);
        dif_ct[i - v[i] + n].insert(v[i]);
    }
    for(int i = 0; i < n; i++) {
        if(sum_ct[i + v[i]].size() < dif_ct[i - v[i] + n].size()) {
            for(int g : sum_ct[i + v[i]]) {
                if(dif_ct[i - v[i] + n].count(v[i] - g)) tot++;
            }
        }
        else {
            for(int g : dif_ct[i - v[i] + n]) {
                if(sum_ct[i + v[i]].count(v[i] - g)) tot++;
            }
        }
    }
    /*
    for(int i = 0; i < n; i++) {
        for(int j = i-1; j >= 0; j--) {
            if(v[j] < v[i] && is_in_range(j + v[i]) && v[j] + v[j + v[i]] == v[i] && v[j + v[i]] == i - j) tot++;
        }
    }
    */
    return tot;
}

vector<int> construct_range(int n, int k) {
    vector<int> v(n);
    for(int i = 0; i < n; i++) {
        v[i] = (i % 3 ? 0 : 1) + 1;
    }
    return v;
}

• Subtask 0: 0 / 0
• Subtask 1: 8 / 8
• Subtask 2: 6 / 6
• Subtask 3: 10 / 10
• Subtask 4: 11 / 11
• Subtask 5: 16 / 16
• Subtask 6: 19 / 19
• Subtask 7: 3 / 5
• Subtask 8: 1.245 / 5
• Subtask 9: 0.4998 / 5
• Subtask 10: 0.2143 / 5
• Subtask 11: 0.25 / 5
• Subtask 12: 0.0833 / 5